The scientists that study this kind of thing try to check for similarities and classify them as the same or different when appropriate.
They probably classify them as different if the time they lived (based on the surrounding rock they were found in) or their bone structures is sufficiently different from anything previously discovered.
It's also a lot easier to merge two classifications rather than split a group into two.
The scientists that study this kind of thing try to check for similarities and classify them as the same or different when appropriate.
They probably classify them as different if the time they lived (based on the surrounding rock they were found in) or their bone structures is sufficiently different from anything previously discovered.
It's also a lot easier to merge two classifications rather than split a group into two.
http://en.wikipedia.org/wiki/Titanosauriformes
http://en.wikipedia.org/wiki/Sauropoda